#include <REGX52.H>
sbit sound=P3^5;
void main()
{
	EA=1;
	ET1=1;
	TMOD=0x10;
	TH1=0xfe;//??500??
	TL1=0x33;
	TR1=1;
	while(1)
	{	}
}
 
void Timer1_Routine() interrupt 3	//	????
{
	TH1=0xfe;
	TL1=0x33;
	sound=~sound;
}